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  <title>Document</title>
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<body>
  
  <script>

    var message = "Hello World"

    // 1.严格的修改字符串, 之前的字符串内部修改掉
    // message[2] = "a"
    // console.log(message)

    // String两个方法:(重要)
    // toUpperCase: 将所有的字符变成大写
    // toLowerCase: 将所有的字符变成小写
    
    // var message1 = message.toUpperCase()
    // console.log(message)
    // console.log("message1:", message1)
    // message = message.toUpperCase()
    
    var message2 = message.toLowerCase()
    console.log(message2)

  </script>

</body>
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